[Omnikaiser]

Rider war I dont know (maybe northern vs southern base. I guess thats possible)

But Kento becoming the big bad/next Calibur for some reason I'm 99% sure.
He has the typical reactions of the good guy becoming bad, wearing purplish clothes already.
He is the only one knowing what Touma can't remember so I expect he changes side before we reach the "but you could have just told him and everything would be okay" point.